https://hal.in2p3.fr/in2p3-00022163Desplanques, B.B.DesplanquesLPSC - Laboratoire de Physique Subatomique et de Cosmologie - UJF - UniversitĂ© Joseph Fourier - Grenoble 1 - Grenoble INP - Institut polytechnique de Grenoble - Grenoble Institute of Technology - IN2P3 - Institut National de Physique NuclĂ©aire et de Physique des Particules du CNRS - Institut Polytechnique de Grenoble - Grenoble Institute of Technology - CNRS - Centre National de la Recherche ScientifiqueTheussl, L.L.TheusslForm factors in the 'point form' of relativistic quantum mechanics : single and two-particle currentsHAL CCSD2004[PHYS.HTHE] Physics [physics]/High Energy Physics - Theory [hep-th][PHYS.HPHE] Physics [physics]/High Energy Physics - Phenomenology [hep-ph]bibliotheque, LPSC2004-08-24 15:18:592023-03-24 14:52:472006-07-12 10:30:22enJournal articles10.1140/epja/i2003-10183-21Electromagnetic and Lorentz-scalar form factors are calculated for a bound system of two spin-less particles exchanging a zero-mass scalar particle. Different approaches are considered including solutions of a Bethe-Salpeter equation, a ``point form'' approach to relativistic quantum mechanics and a non-relativistic one. The comparison of the Bethe-Salpeter results, which play the role of an ``experiment'' here, with the ones obtained in ``point form'' in single-particle approximation, evidences sizable discrepancies, pointing to large contributions from two-body currents in the latter approach. These ones are constructed using two constraints: ensuring current conservation and reproducing the Born amplitude. The two-body currents so obtained are qualitatively very different from standard ones. Quantitatively, they turn out not to be sufficient to remedy all the shortcomings of the ``point form'' form factors evidenced in impulse approximation.